Generally, a fuel cap may include a click device to prevent the fuel cap from over tightening when a user is closing a fuel tank with the fuel cap. The click device will generate a click sound to alert the user if the fuel cap is further rotated by the user after the fuel cap is tightened. However, when opening the fuel cap, the user may not know that the fuel cap has been unlocked and the continued rotation may cause damage on the parts, especially for the fuel cap that is released by a half turn. U.S. Pat. No. 7,516,867B2 discloses a fuel cap having a torque element and a click device which are independent each other. However, the disclosed click device is complicated in its structure.